Chelating compounds and their use

ABSTRACT

A chelating compound of the formula: 
     
         (R-NHOC-CH.sub.2).sub.n --A--(CH.sub.2 COOH).sub.m         (I) 
    
     wherein R is an aromatic ring-containing organic group, A is a residue of an aminopolyacetic acid excluding acetic acid groups (--CH 2  COOH) therefrom, m is an integer of at least two and n is an integer of 1 or 2, or its salt, which has a specificity to a hepatobiliary system so that a complex formed between said chelating compound and a metallic element through a covalent bond is useful as a diagnostic or therapeutic agent for hepatobiliary organs and tissues.

The present invention relates to chelating compounds and their use. More particularly, it relates to chelating compounds having a chelating property and a specificity or selectivity for a hepatobiliary system, and their use as carriers for metal elements suitable for diagnosis or thereby of hepatobiliary organs or tissues.

In recent years, patients suffered from diseases in a hepatobiliary system such as hepatoma are significantly increased, and it is highly demanded to establish a reliable diagnostic method, particularly through imaging, as well as an effective therapeutic method.

Among various imaging agents for hepatobiliary organs or tissues as heretofore reported, there is known technetium-99m-N-pyridoxyl-5-methyltryptophan (Tc-99m-PMT). Imaging with this complex is well evaluated in showing a significant specificity to hepatocellular carcinoma (Hasegawa et al.: Cancer, 57, 230-236 (1986)). Unfortunately, its sensitivity is however somewhat low as 60%. Diethylenetriaminepentaacetato gadolinium (Gd-DTPA) is also known as a nuclear magnetic resonance (NMR) imaging agent (Weinmann et al.: AJR, 142, 619-629 (1984)). However, it is excreted into urine so quickly that its distribution in liver is insufficient and satisfactory informations on liver are hardly obtainable.

As well known, aminopolycarboxylic acids have an excellent chelating property and are useful as carriers for metallic elements suitable for diagnosis. Thus, the complex formed between aminopoly-carboxylic acids and metallic elements are used as imaging agents for radioactive diagnosis, nuclear magnetic resonance (NMR) diagnosis, etc.

It has now been found that the introduction of a certain aromatic ring-containing organic group into an aminopolycarboxylic acid is effective in enhancing the specificity or selectivity for a hepatobiliary system. For instance, when DTPA (diethylenetriaminepentaacetic acid) is administered intravenously into an animal, it is mainly excreted into urine. In contrast, it was experimentally confirmed that N,N"-bis[(2-dansylaminoethyl)carbamoylmethyl]-diethylene-triamine-N,N',N"-triacetic acid (B-DNS-etn-DTPA) obtained by introducing two dansyl groups into DTPA is excreted mainly into intestine through a hepatobiliary system.

As stated above, aminopolycarboxylic acids are well known chelating compounds. Since the covalent bond formed between aminopolycarboxylic acids and metallic elements are generally stable in an animal or at a physiogical pH range, they are practically used as carriers for metallic elements to make imaging agents, for instance, Gd-DTPA as above mentioned. However, it has never been known that their specificity or selectivity for a hepatobiliary system is significantly enhanced by introducing a certain aromatic ring-containing organic group therein.

SUMMARY OF THE INVENTION

The present invention is based on the above finding and provides a chelating compound which has a high specificity or selectivity for a hepatobiliary system and is useful as a carrier for a metallic element to give a diagnostic or therapeutic agent for hepatobiliary organs and tissues.

The chelating compound of the invention is an aminopolycarboxylic acid, particularly an aminopolyacetic acid, in which one or two carboxylic groups are each combined with an aromatic ring-containing organic group, particularly through an amide (--CONH--) bond and at least two carboxylic groups are each kept in a free or salt form to have a chelating property with a metallic element.

More specifically, the chelating compound is representable by the formula:

    (R--NHOC--CH.sub.2).sub.n --A--(CH.sub.2 --COOH).sub.m     (I)

wherein R is an aromatic ring-containing organic group, A is a residue of an aminopolyacetic acid excluding acetic acid groups (--CH₂ COOH) therefrom, m is an integer of at least two and n is an integer of at least one. The carboxyl groups therein may be in a free or salt form.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a scintigram of hepatoma-transplanted rat using In-111-B-DMS-etn-DTPA (70 hours after administration) obtained in Example 12. In FIG. 1, A denotes a tumor.

DETAILED DESCRIPTION

The aminopolyacetic acid comprises a hydrocarbon chain in a straight, branched or cyclic form, at least two amino groups introduced in the hydrocarbon chain (such as --C--NH--C--) and/or at the end of the hydrocarbon chain (such as --C--NH₂), and each of at least three acetic acid groups (--CH₂ --COOH) attached to a nitrogen atom in said amino groups. For example, such aminopolyacetic acid includes ethylenediamine-tetraacetic acid (EDTA), diethylenetriamine pentaacetic acid (DTPA), trans-1,2-cyclohexadiamine tetraacetic acid (CyDTA), 1,4,7,10-tetraazacyclododecane tetraacetic acid (DOTA), etc. As to other specific examples of the aminopolyacetic acid, reference may be made to JP-A-58/29718 (DE-A-3129906).

In the chelating compound of the invention, at least two acetic acid groups originated from the aminopolyacetic acid are kept in a free or salt form such as an alkali metal salt so as to capture a metallic element through a covalent bond, while at least one acetic acid group is combined with the aromatic ring-containing organic group. Preferably, the aromatic ring-containing organic group is originated from an aromatic ring-containing organic amine, and the combination between the aminopolyacetic acid and the aromatic ring-containing organic amine is made through a carbonamide (--CONH--) linkage.

As the aromatic ring-containing organic group, there are exemplified aryl, aryl(lower)alkyl, arylsulfonyl, aryl(lower)alkylsulfonyl, arylamino(lower)alkyl, aryl(lower)alkylamino(lower)alkyl, arylsulfonylamino(lower)alkyl, aryl(lower)alkylsulfonylamino(lower)alkyl, etc. The aryl portion, of which examples are phenyl, naphthyl, etc., in these groups may be optionally substituted with lower alkyl (e.g. methyl, ethyl), lower alkylamino (e.g. methylamino, ethylamino), di(lower)alkylamino (e.g. dimethylamino, diethylamino), etc. Thus, specific examples of the aromatic ring-containing organic group represented by the symbol R are phenyl, lower alkylphenyl such as tolyl (e.g. p-tolyl), di(lower)alkylaminophenyl such as dimethylaminophenyl (e.g. p-dimethylaminophenyl), phenyl(lower)alkyl such as phenethyl, benzenesulfonylamino(lower)alkyl such as benzenesulfonylaminoethyl, lower alkylbenzenesulfonylamino(lower)alkyl such as toluenesulfonylaminoethyl (e.g. p-toluenesulfonylaminoethyl), di(lower)alkylaminonaphthalenesulfonylamino(lower)alkyl such as dimethylaminonaphthalenesulfonylaminoethyl or dimethylaminonaphthalenesulfonylaminohexyl, naphthylamino(lower)alkyl such as naphthylaminoethyl, naphthyl(lower)alkyl such as naphthylmethyl, naphthalenesulfonylamino(lower)alkyl such as naphthalenesulfonylaminoethyl, etc., among which naphthyl(lower)alkyl, naphthylamino(lower)alkyl, naphthalenesulfonylamino(lower)alkyl, 5-dimethylaminonaphthalene-1-sulfonylamino(lower)alkyl (i.e. dansylamino(lower)alkyl), etc. are favorable.

Production of the chelating compound of the invention may be achieved by a per se conventional procedure for formation of an amide bond between an amino group and a carboxyl group, for instance, reacting an aromatic ring-containing organic amine of the formula: R--NH₂ (wherein R is as defined above) with an aminopolyacetic acid of the formula: (HOOCCH₂)_(n) --A--(CH₂ COOH)_(m) (wherein A, m and n are each as defined above) in any reactive form. The reaction may be carried out usually in an inert solvent (e.g. tetrahydrofuran, dioxane, dimethylformide, benzene, toluene), if necessary, in the presence of the agents such as a base, a dehydrating agent, etc. to condense. Depending on the reaction conditions, particularly the proportion of the aromatic ring-containing organic amine to the aminopolyacetic acid, there is produced the desired chelating compound having one or two aromatic ring-containing organic groups as the major product. When their mixture is obtained, the mono-substituted product and the bis-substituted product can be easily separated by a per se conventional separation procedure such as chromatography. In general, the bis-substituted product is favorable, because of its higher specificity or selectivity for a hepatobiliary system.

The thus obtained chelating compound can be converted into the corresponding complex by treatment with a metal element in a per se conventional procedure for complexation. The kind of the metal element may be appropriately chosen depending on the purpose for which the complex is used.

For the nuclear medicine such as scintigraphical diagnosis or radio therapy, various radioactive metal elements may be used. For instance, the use of such gamma-ray emitting metal elements as technetium-99m, indium-111 and gallium-67 are preferred in order to produce tumor-imaging agents. On the other hand, beta-ray emitting metal elements such as rhenium-186, rhenium-188 and yttrium-90 are clinically useful for treatment of tumors.

For instance, B-DNS-etn-DTPA as an example of the invention is promptly excreted from the normal or healthy liver to bile ducts, but when a tumor is present in liver, it is difficulty excreted to bile ducts, because no efficient bile duct exists in the tumor lesion. Utilizing this dynamic behavior, a complex of B-DNS-etn-DTPA with indium-111 is used as a radioactive imaging agent for diagnosis of a hepatobiliary system, and a complex of B-DNS-etn-DTPA with rhenium-186 may be employed to irradiate the tumor lesion in liver for the therapeutic purpose.

Metallic elements usable for NMR imaging are required to be paramagnetic, and their preferred examples are lanthanoid elements under Atomic Nos. 57 to 70 and transition metal atoms under Atomic Nos. 21 to 29, 42 and 44. Among them, gadolinium, dysprosium, etc. are especially preferred because of their strong magnetic moment and chemical stability. These paramagnetic metallic elements are often toxic in concentrations required for NMR imaging, and therefore their amounts to be introduced into animals are desired to be kept as little as possible. The administration of those paramagnetic metallic elements in the form of complexes with the chelating compounds of the invention is quite advantageous, because the toxicity of the metallic elements are suppressed by the complexation and also their amounts to be administered for effective NMR imaging are lowered due to their specificity assuring an efficient accumulation at the target organ or tissue in a hepatobiliary system.

For instance, diethylenetriamine-pentaacetato gadolinium(III) (Gd-DTPA) is normally administered on the clinical use by intravenous injection at a dose of 100 μmol/kg. Since its distribution is not however specific for a hepatobiliary system, the excretion into urine is made promptly. As the result, sufficient contrast useful for diagnosis can be obtained only over a period of time producing the differences in concentration among tissues or organs. In fact, the administation of Gd-DTPA to rats at a dose of 50 μmol/mg does not produce any change of signal intensity in liver (Kawamura et al.:Image Information, 21, 206-207 (1989)). Administration of a complex of Gd(III) with N-[(2-dansylaminoethyl)carbamoylmethyl]-diethylenetriamine-N,N',N",N"-tetraacetic acid (Gd(III)-DNS-etn-DTPA) to rats produces enhancement of the T₁ relaxation in liver even at such a small dose as 20 μmol/kg, and this effect remains for one hour after the administration. Thus, Gd(III)-DNS-etn-DTPA is specifically taken up into liver so that satisfactory NMR imaging can be obtained even at a low dose.

When the use for X-ray diagnosis is aimed at, the chelating compound of the invention may be complxed with a metallic element from Atomic Nos. 57 to 83, particularly lanthanum to form a complex.

Practical and presently preferred embodiments of the invention are illustratively shown on the following Examples.

EXAMPLE 1 Preparation of N-[(2-dansylaminoethyl)carbamoylmethyl]-diethylenetriamine-N,N',N",N"-tetraacetic acid (DNS-etn-DTPA) (2) and N,N"-bis[(2-dansylaminoethyl)-carbamoylmethyl]-diethylenetriamine-N,N',N"-triacetic acid (B-DNS-etn-DTPA) (3) A. N-Dansyl-ethylenediamine (1) ##STR1##

To a solution of ethylenediamine (635 mg, 10.6 mmol) in chloroform (10 ml), a solution of dansyl chloride (285 mg, 1.06 mmol) in chloroform (12 ml) was dropwise added, and the reaction mixture was stirred at room temperature overnight, followed by addition of a bit of 1N sodium hydroxide thereto for hydrolysis of unreacted dansyl chloride. The reaction mixture was concentrated, and the residue was combined with acetone. Insoluble materials were removed by filtration, and the filtrate was concentrated. Water (50 ml) was added to the residue, and extracted with ethyl acetate three times. The organic layer was dried over anhydrous sodium sulfate and concentrated. The residue was dissolved in a small amount of ethyl acetate, a bit of n-hexane was added thereto, and the resultant mixture was allowed to stand at room temperature overnight. The precipitate was collected and recrystallized from ethyl acetate to give Compound (1) (124 mg). Yield, 63%.

B. DNS-etn-DTPA (2) and B-DNS-etn-DTPA (3) ##STR2##

Diethylenetriamine-N,N,N',N",N"-pentaacetic acetic anhydride (DTPA) (1.39 g, 3.89 mmol) was dissolved in dimethylformamide (30 ml) with heating, and the resultant solution was cooled to room temperature. A solution of Compound (1) (113 mg, 0.385 mmol) in dimethylformamide (5 ml) was dropwise added thereto with stirring, and the reaction was carried out at room temperature for 1.5 hours. After concentration, the residue was combined with 0.1M carbonate buffer (pH 9.0, 20 ml) and carried out on anionic resin exchange chromatography (resin: AG-X4; eluent: 0.3-3M formic acid) and thin layer chromatography (supporting layer: silica gel 60; developing solvent: ethanol/aqueous ammonia=4/1) for purification, whereby Compound (2) (69 mg) and Compound (3) (72 mg) respectively in yields of 27% and 20%.

Compound (2):

IR (KBr) cm⁻¹ : SO₂ --NH (1140, 1320), COO⁻ (1400, 1590), CO--NH (1660, 3420), C₁₀ H₆ --N--(CH₃)₂ (2800), CH₂ (2950).

FAB-MS (negative): m/z 667 (M--H)⁻, m/z 689 (M+Na--2H)⁻, m/z 711 (M+2Na--3H)⁻.

Elemental analysis for C₂₈ H₃₈ N₆ O₁₁ S₁ Na₂. 41/2H₂ O (%): Calcd.: C, 42.37; H, 5.97; N, 10.59; S, 4.04. Found: C, 41.94; H, 5.70; N, 10.99; S, 4.06.

Compound (3):

IR (KBr) cm⁻¹ : SO₂ --NH (1140, 1320), COO⁻ (1410, 1590), CO--NH (1660, 3400), C₁₀ H₆ --N--(CH₃)₂ (2800), CH₂ (2950).

FD-MS: m/z 945 (M+H).

Elemental analysis for C₄₂ H₅₄ N₉ O₁₂ S₂ Na₃.8H₂ O (%): Calcd.: C, 43.71; H, 6.11; N, 10.92; S, 5.56. Found: C, 43.54; H, 5.52; N, 10.51; S, 5.89.

EXAMPLE 2 Preparation of N-[(6-dansylaminohexyl)carbamoylmethyl]-diethylenetriamine-N,N',N",N"-tetraacetic acid (DNS-hxn-DTPA) (5) and N,N"-bis[(6-dansylaminohexyl)-carbamoylmethyl]-diethylenetriamine-N,N',N"-triacetic acid (B-DNS-hxn-DTPA) (6) A. N-Dansyl-hexamethylenediamine (4) ##STR3##

Hexamethylenediamine (5.39 g, 45.9 mmol) was combined with dimethylformamide (15 ml), and a solution of dansyl chloride (2.40 g, 8.7 mmol) in dimethylformamide (10 ml) was dropwise added thereto, followed by stirring at room temperature for 4 hours. Insoluble materials were removed by filtration, and the filtrate was stirred at room temperature overnight. After concentration, water and ethyl acetate were added to thereto, and 1N hydrochloric acid was added thereto to adjust the aqueous layer to pH 4. The aqueous layer was washed with ethyl acetate three times, adjusted to pH 11 with potassium carbonate and extracted with ethyl acetate twice. The extracts were collected, washed with water three times, dried over anhydrous sodium sulfate and concentrated to give Compound (4) (1.04 g) as an oil. Yield, 34%.

B. DNS-hxn-DTPA (5) ##STR4##

DTPA anhydride (777 mg, 2.18 mmol) was dissolved in dimethylformamide (20 ml) under heating, and the resultant solution was cooled to room temperature. A solution of Compound (4) (130 mg, 0.372 mmol) in dimethylformamide (5 ml) was dropwise added thereto with stirring, and the reaction was carried out at room temperature for 1 hour. After concentration, the residue was combined with 1M carbonate buffer (pH 9.0, 50 ml) and allowed to stand in a refrigerator overnight. Insoluble materials were removed by filtration, and the filtrate was treated in the same manner as in Example 1 B. to give Compound (5) (47 mg). Yield, 17 %.

Compound (5)

IR (KBr) cm⁻¹ : SO₂ --NH (1140, 1320), COO⁻ (1410, 1590), CO--NH (1660, 3420), C₁₀ H₆ --N--(CH₃)₂ (2800), CH₂ (2950).

FAB-MS (negative): m/z 745 (M+Na--2H)⁻, m/z 761 (M+K--2H)⁻, m/z 767 (M+2Na--3H)⁻, m/z 783 (M+Na+K--3H)³¹.

Elemental analysis for C₃₂ H₄₆ N₆ O₁₁ S₁ Na₂.6H₂ O (%): Calcd.: C, 43.83; H, 6.67; N, 9.58; S, 3.66. Found: C, 43.24; H, 6.43; N, 10.35; S, 3.73.

C. B-DNS-hxn-DTPA (6) ##STR5##

The insoluble materials as removed in the above B were collected and dissolved in methanol. The resultant solution was concentrated, and the residue was carried out on thin layer chromatography for purification, whereby Compound (6) (24 mg) was obtained. Yield, 6%.

Compound (6):

IR (KBr) cm⁻¹ : SO₂ --NH (1140, 1310), COO⁻ (1400, 1580), CH₂ (1450, 2930), ##STR6## CO--NH (1660, 3400), C₁₀ H₆ --N--(CH₃)₂ (2780).

FAB-MS (negative): m/z 1054 (M--H)⁻, m/z 1076 (M+Na--2H)⁻ m/z 1092 (M+K--2H)⁻.

Elemental analysis for C₅₀ H₇₁ N₉ O₁₂ S₂ Na₂.7H₂ O (%): Calcd.: C, 48.97; H, 6.99; N, 10.28; S, 5.23. Found: C, 48.56; H, 6.44; N, 10.01; S, 5.05.

EXAMPLE 3 Preparation of N-[[2-(1-naphthylamino)ethyl]-carbamoylmethyl]-diethylenetriamine-N,N', N",N"-tetraacetic acid (8) A. N-1-Naphthylethylenediamine (7) ##STR7##

To a suspension of N-1-naphthylethylenediamine dihydrochloride (746 mg, 2.88 mmol) in chloroform (50 ml), a saturated solution of sodium hydrogen carbonate (50 ml) was added, and the resultant mixture was stirred. The organic layer was collected, washed with a saturated solution of sodium chloride twice, dried over anhydrous sodium sulfate and concentrated to give Compound (7) (310 mg) as an oil. Yield, 58%.

B. N-[[2-(1-Naphthylamino)ethyl]carbamoylmethyl]-diethylenetriamine-N,N',N",N"-tetraacetic acid (8) ##STR8##

DTPA anhydride (2.02 g, 5.60 mmol) was dissolved in dimethylformamide (20 ml) with heating and cooled to room temperature. A solution of Compound (7) (218 mg, 1.17 mmol) in acetone (5 ml) was added thereto with stirring, and the reaction was carried out at room temperature for 1.5 hours. The resultant mixture was allowed to stand at room temperature in a dark box overnight. The reaction mixture was treated with activated charcoal and concentrated. To the residue, 0.1M carbonate buffer (pH 8.9, 20 ml) was added, and the resultant mixture was treated with activated charcoal, followed by concentration. The residue was dissolved in 0.1M carbonate buffer (pH 8.9, 15 ml), treated with activated charcoal and carried out on anionic exchange resin chromatography (resin: AG-X4, eluent: 1.2-4.8M formic acid) and thin layer chromatography to give Compound (8) (34 mg). Yield, 5%.

Compound (8):

IR (KBr) cm⁻¹ : COO⁻ (1400, 1580), CO--NH (1660, 3400), CH₂ (2960).

FAB-MS (positive): m/z 606 (M+2Na--H)⁺, m/z 622 (M+K+Na--H)⁺, m/z 650 (M+4Na--3H)⁺.

Elemental analysis for C₂₆ H₃₃ N₅ O₉ Na₂.6H₂ O (%): Calcd.: C, 43.76; H, 6.36; N, 9.81. Found: C, 43.81; H, 6.09; N, 10.58.

EXAMPLE 4 Preparation of N,N"-bis(1-naphthylmethylcarbamoylmethyl)-diethylenetriamine-N,N',N",N"-triacetic acid (9) ##STR9##

DTPA anhydride (2.05 g, 5.74 mmol) was dissolved in hot dimethylformamide (20 ml) with heating and cooled to room temperature. A solution of 1-naphthalenemethylamine (467 mg, 2.88 mmol) in acetone (5 ml) was dropwise added thereto, and the resultant mixture was stirred at room temperature for 2 hours. After concentration, 0.1M carbonate buffer (pH 8.9, 30 ml) was added to the residue. Insoluble materials were collected, dissovled in methanol with heating and then cooled. After removal of insoluble materials by filtration, the filtrate was concentrated. The residue was dissolved in a small amount of dimethylformamide and carried out on thin layer chromatograph for purification, whereby Compound (9) (114 mg) was obtained. Yield, 6%.

Compound (9)

IR (KBr) cm⁻¹ : COO⁻ (1400, 1590), ##STR10## CO--NH (1650, 3400), CH₂ (2950).

FAB-MS (positive): m/z 710 (M+K)⁺, m/z 732 (M+K+Na--H)⁺, m/z 748 (M+2K--H)⁺.

Elemental analysis for C₃₆ H₄₀ N₅ O₈ Na₁.5H₂ O (%): Calcd.: C, 55.17; H, 6.43; N, 8.94. Found: C, 54.82; H, 6.08; N, 9.65.

EXAMPLE 5 Preparation of N-[[2-(1-naphthalenesulfonylamino)-ethyl]carbamoylmethyl]-diethylenetriamine-N,N',N",N"-tetraacetic acid (11) A. N-(1-Naphthalenesulfonyl)-ethylenediamine (10) ##STR11##

To a solution of ethylenediamine (1.06 g, 17.6 mmol) in dimethylformamide (10 ml), triethylamine (1.79 g, 17.7 mmol) was added, followed by stirring. With stirring at room temperature, a solution of 1-naphtalenesulfonyl chloride (4.00 g, 17.6 mmol) in dimethylformamide (15 ml) was dropwise added thereto, and the reaction was carried out in an ice bath for 1 hour. Insoluble materials were removed by filtration, and the filtrate was concentrated. To the residue, chloroform and water were added, and insoluble materials were filtered off. Furthermore, the aqueous layer was separated, washed with ethyl acetate twice and adjusted to pH 11 with potassium carbonate, followed by extraction with ethyl acetate three times. The extracts were collected, washed with water twice, dried over anhydrous sodium sulfate and concentrated. The residue was allowed to stand in a regrigerator overnight, and the precipitate was collected and recrystallized from ethyl acetate to give Compound (10) (153 mg). Yield, 4%.

B. N-[[2-(1-Naphthalenesulfonylamino)ethyl]-carbamoylmethyl]-diethylenetriamine-N,N',N",N"-tetraacetic acid (11) ##STR12##

DTPA anhydride (996 mg, 2.79 mmol) was dissolved in dimethylformamide (20 ml) with heating, and the resultant solution was cooled to room temperature. A solution of Compound (10) (139 mg, 0.557 mmol) in acetone (20 ml) was dropwise added thereto at room temperature with vigorous stirring. After the addition, the resultant mixture was stirred at room temperature for 1 hour and then allowed to react overnight. After concentration, the residue was dissolved in 0.1M carbonate buffer (pH 8.9, 15 ml) and then treated in the same manner as in Example 1 B to give Compound (11) (66 mg). Yield, 19%.

Compound (11):

IR (KBr) cm⁻¹ : SO₂ --NH (1160, 1320), COO⁻ (1400, 1590), CH₂ (2870), CO--NH (3420).

FAB-MS (negative): m/z 646 (M+Na--2H)⁻, m/z 662 (M+K+2H)⁻, m/z 668 (M+2Na--3H)⁻, m/z 684 (M+Na+K--3H)⁻.

Elemental analysis for C₂₆ H₃₄ N₅ O₁₁ S₁ Na₁.6H₂ O (%): Calcd.: C, 41.32; H, 6.14; N, 9.27; S, 4.24. Found: C, 41.05; H, 5.55; N, 9.96; S, 4.23.

From the results of the elemental analysis as above, the products in Examples 1 to 11, i.e. Compounds (2), (3), (5), (6), (8), (9) and (11), were obtained in the form of sodium salt. This is probably due to sodium salt in the supporting layer used in thin layer chromatography at the stage of purification.

EXAMPLE 6 In-111-DNS-etn-DTPA (complex) A. Preparation of In-111 Complex with Compound (2)

Compound (2) (0.93 mg, 1.39 μmol) was dissolved in 0.2M acetate buffer (pH 5.3, 0.46 ml), and the similar buffer (pH 5.3, 0.46 ml) containing indium chloride (¹¹¹ In, 69.1 MBq) was added thereto. The resultant mixture was shaken for 30 seconds to give In-111-DNS-etn-DTPA.

B. Behavior of In-111-DNS-etn-DTPA on Thin Layer Chromatography

An appropriate amount of In-111-DNS-etn-DTPA was spotted onto a silica gel plate (silica gel 60 manufactured by Merck Co., Ltd.) at a distance of 2 cm from the bottom and developed for 10 cm using a mixture of methanol-acetic acid (5:3) as a developing solvent. After air-drying, the the plate was scanned with a thin layer radiochromatoscanner (Aloca Co.) to determine the distribution of radioactivity, and the radiochemical purity was calculated with a data processing apparatus (D-2000, manufactured by Hitachi Ltd.).

As the result, a single radioactivity peak (Rf=0.13) was observed. Since the Rf value of this peak is different from that (Rf=0) of indium acetate (¹¹¹ In) or indium chloride (¹¹¹ In) as a possible radiochemical impurity, the radiochemical purity of In-111-DNS-etn-DTPA was determined to be 100%.

C. Behavior of In-111-DNS-etn-DTPA on Electrophoresis

An appropriate amount of In-111-DNS-etn-DTPA was spotted on an acetylated cellulose membrane and subjected to electrophoresis using 50 mM phosphate buffer (pH 7.4) with a constant current of 1 mA/cm at room tempeature for 30 minutes. In the same manner as in the above B, the membrane was scanned with a thin layer radiochromatoscanner to determine the distibution of radioactivity. As the result, it was revealed that In-111-DNS-etn-DTPA is a complex having a single negative charge.

EXAMPLE 7 Other In-111 Complexes

In the same manner as in Example 6 A, B and C, In-111 complexes with Compounds (3), (5), (6), (8), (9) and (11) were prepared, and their behaviors on thin layer chromatography (TLC) and electrophoresis (EP) as well as their radiochemical purity were determined. The results are shown in Table 1.

                  TABLE 1                                                          ______________________________________                                         Carrier                       Radiochemical                                    compound                                                                               TLC (Rf)     EP       purity (%)                                       ______________________________________                                         (3)     0.12         --       100                                              (5)     0.14         Negative 100                                              (6)     0.08         --       100                                              (8)     0.19         Negative 100                                              (9)     0.20         Positive 100                                              (11)    0.24         Negative 100                                              ______________________________________                                    

EXAMPLE 8 Gd-DNS-etn-DTPA (Complex)

Compound (2) (21.0 mg, 31.4 μmol) was dissolved in 0.2M acetate buffer (pH 5.3, 5 ml), and 1.97 ml of a 10⁻³ N hydrochloric acid (10.5 ml) containing GdCl₃.6H₂ O (93.3 mg, 0.251 mmol) were added thereto. The resultant mixture was shaken for 1 minute and concentrated. The residue was dissolved in water (2 ml) and subjected to high performance liquid chromatography for purification, followed by lyophilization to give Gd-DNS-etn-DTPA (20.3 mg). Yield, 79%.

IR (KBr) cm⁻¹ : SO₂ --NH (1150, 1320), COO⁻ (1410, 1590), C₁₀ H₆ --N--(CH₃)₂ (2800), CH₂ (2950), CO--NH (3400).

FAB-MS (positive): m/z 823 M⁺, m/z 845 (M+Na--H)⁺.

Elemental analysis for C₂₈ H₃₇ N₆ O₁₁ S₁ Gd₁.9H₂ O (%): Calcd.: C, 34.1; H, 5.6; N, 8.5; S, 3.3. Gd, 16.0. Found: C, 33.4; H, 4.7; N, 8.4; S, 3.5; Gd, 15.4.

EXAMPLE 9 Eu-DNS-etn-DTPA (Complex) and La-DNS-etn-DTPA (Complex)

In the same manner as in Example 8 but using EuCl₃.6H₂ O or LaCl₃.7H₂ O, the Eu or La complex with Compund (2) was prepared. There was thus obtained Eu-DNS-etn-DTPA (19.4 mg) in a yield of 77% or La-DNS-etn-DTPA (14.4 mg) in a yield of 61%.

Eu-DNS-etn-DTPA:

IR (KBr) cm⁻¹ : SO₂ --NH (1150, 1330), COO⁻ (1410, 1600), C₁₀ H₆ --N--(CH₃)₂ (2800), CH₂ (2960), CO--NH (3420).

FAB-MS (negative): m/z 817 (M--H)⁻.

Elemental analysis for C₂₈ H₃₇ N₆ O₁₁ S₁ Eu₁.71/2H₂ O (%): Calcd.: C, 35.3; H, 5.5; N, 8.8; S, 3.4; Eu, 15.9. Found: C, 35.1; H, 4.6; N, 8.7; S, 4.0; Eu, 15.0.

La-DNS-etn-DTPA:

IR (KBr) cm⁻¹ : SO₂ --NH (1150, 1330), COO⁻ (1410, 1590), C₁₀ H₆ --N--(CH₃)₂ (2800), CH₂ (2950), CO--NH (3420).

FAB-MS (negative): m/z 803 (M--H)⁻.

Elemental analysis for C₂₈ H₃₇ N₆ O₁₁ S₁ La₁.8H₂ O (%): Calcd.: C, 35.4; H, 5.6; N, 8.9; S, 3.4; La, 14.6 Found: C, 34.7; H, 4.4; N, 8.7; S, 2.9; La, 13.7.

EXAMPLE 10 Radioactivity Distribution of In-111-DNS-etn-DTPA and In-111-B-DNS-etn-DTPA in Rats on Intravenous Injection

In-111-DNS-etn-DTPA or In-111-B-DNS-etn-DTPA was intravenously injected to Sprague-Dawley rats (female) at a dose of 25 μg/rat, and the rats were sacrificed one hour thereafter to take out various organs. The radioactivity in each organ was measured, and the results are shown in Table 2.

                  TABLE 2                                                          ______________________________________                                         Radioactivity distribution of In-111-DNS-etn-DTPA                              and In-111-B-DNS-etn-DTPA in rats (% injected dose/organ)                                    In-111-DNS-                                                                               In-111-B-DNS-                                         Organ         etn-DTPA   etn-DTPA                                              ______________________________________                                         Liver         1.35       2.60                                                  Bowel         68.01      91.86                                                 Kidney        1.00       0.26                                                  Urinary bladder                                                                              25.49      3.86                                                  Blood (1 ml)  0.06       0.03                                                  Others        7.97       2.74                                                  ______________________________________                                    

From the above results, it is suggested that In-111-B-DNS-etn-DTPA is an excellent radioactive diagnostic agent for examination of hepatobiliary tissues.

For comparison, the radioactivity distribution of In-111-DTPA (In-111 complex with DTPA), prepared as in Example 6 A, in rats on intravenous injection was determined as above. As the result, it was revealed that about 90% of the injected radioactivity was excreted in urine within one hour after the administration.

It is thus found that the excretion route of DTPA is changed to a hepatobiliary system by introduction of a dansyl group therein. In other words, a dansyl group may be concluded to be effective in the construction of a hapatobiliary tissue-specific carrier.

EXAMPLE 11 Radioactivity Distribution of In-111-DNS-hxn-DTPA and In-111-B-DNS-hxn-DTPA in Rats on Intravenous Injection

In-111-DNS-hxn-DTPA or In-111-B-DNS-hxn-DTPA was intravenously injected to Sprague-Dawley Rats (female) at a dose of 25 μg/rat, and the rats were sacrificed one hour thereafter to take out various organs. The radioactivity in each organ was measured, and the results are shown in Table 3.

                  TABLE 3                                                          ______________________________________                                         Radioactivity distribution of In-111-DNS-hxn-DTPA                              and In-111-B-DNS-hxn-DTPA in rats (% injected dose/organ)                                    In-111-DNS-                                                                               In-111-B-DNS-                                         Organ         hxn-DTPA   hxn-DTPA                                              ______________________________________                                         Liver         0.51       1.82                                                  Bowel         93.42      92.81                                                 Kidney        0.05       0.12                                                  Urinary bladder                                                                              5.35       0.46                                                  Blood (1 ml)  0.01       0.05                                                  Others        0.65       4.45                                                  ______________________________________                                    

From the above results, it is found that like In-111-B-DNS-etn-DTPA, tested In-111 complexes are both excellent diagnostic agents for hepatobiliary tissues.

EXAMPLE 12 Imaging of Rat Hepatoma in Rat with In-111-B-DNS-etn-DTPA

In-111-B-DNS-etn-DTPA was injected into a hepatoma-transplanted WKA-rat (male, tumor size: about 3 cm) intravenously injected at a dose of 50 μg/rat and kept in a cage for 70 hours. The rat was fixed and subjected to image with a gamma-camera (manufactured by Toshiba, Ltd.). The posterior scintigram thus obtained in shown in FIG. 1 of the accompanying drawings. While the radioactivity was taken up in liver and bowel, the tumor (at the left shoulder of the rat) was clearly visualized.

From the above results, it is clear that In-111-B-DNS-etn-DTPA is taken up into hepatoma.

EXAMPLE 13 A. Relaxation of Gd-DNS-etn-DTPA

Gd-DNS-etn-DTPA as obtained in Example 8 was dissolved in 10 mM acetate buffer (pH 5.5), and the relaxation time (T₁ and T₂, millisecond) was measured with regard to water proton by NMR (manufactured by Nihon Denshi; 270 MHz; 25° C.). The results are shown in Table 4.

                  TABLE 4                                                          ______________________________________                                         Concentration                                                                  (mM)              T.sub.1 T.sub.2                                              ______________________________________                                         5.59               44      36                                                  1.31              313     246                                                  0.66              534     424                                                  0                 3260    1315                                                 ______________________________________                                    

From the above results, Gd-DNS-etn-DTPA shows an excellent relaxation time. For instance, the T₁ and T₂ values of water were shortened about 74 times and about 37 times at a concentration of 5.59 mM, respectively.

B. Pharmacodynamics on Relaxation of Gd-DNS-etn-DTPA in Mice

To each of ICR mice (female), a solution of Gd-DNS-etn-DTPA in 10 mM acetate buffer (pH 5.5) was intravenously administered at a dose of 0.02 mM/kg by injection. The mice were sacrificed by cutting their necks at 1 minute, 1 hour and 6 hours after the adminsitration. The proton relaxation value of each selected organ was measured in a test tube by NMR (270 MHz) at 25° C. Relaxation of T₁ and T₂ on each organ is shown in Table 5.

                  TABLE 5                                                          ______________________________________                                                     Time                                                                             After     After     After                                        Normal value  1 min.    60 min.   360 min.                                     Organ  T.sub.1 T.sub.2                                                                               T.sub.1                                                                              T.sub.2                                                                            T.sub.1                                                                              T.sub.2                                                                            T.sub.1                                                                              T.sub.2                        ______________________________________                                         Liver  1040    17     776   16   745  17  1025  19                             Heart  1484    29     1289  28  1408  26  1523  29                             Kidney 1269    31     918   28   878  29  1196  33                             Brain  1576    45     1556  --  1586  51  1613  50                             Blood  1755    53     884   --  1713  67  1680  54                             ______________________________________                                    

From the above results, it is revealed that Gd-DNS-etn-DTPA is quickly taken up by liver, kidney and heart in mouse and excreted. Since the change of T₁ in liver and kidney with time is distinguished from that of T₁ in blood, the behavior of Gd-DNS-etn-DTPA in liver and kidney may be considered to be not originated from that in blood. Furthermore, Gd-DNS-etn-DTPA may be found to afford an influence on the T₁ relaxation in a living body. 

What is claimed is:
 1. A chelating compound of the formula:

    (R--NHOC--CH.sub.2).sub.n --A--(CH.sub.2 COOH).sub.m

wherein R is an aromatic ring-containing organic group, A is a residue of an aminopolyacetic acid excluding acetic acid groups therefrom, m is an integer of 2 to 4 and n is an integer of 1 or 2, or its salt, wherein the aromatic ring-containing organic group is aryl, aryl(lower)alkyl, arylsulfonyl, aryl(lower)alkylsulfonyl, arylamino(lower)alkyl, aryl(lower)alkylamino(lower)alkyl, arylsulfonylamino(lower)alkyl or aryl(lower)alkylsulfonylamino(lower)alkyl, the aryl moiety being naphthyl which can be substituted with lower alkyl, lower alkylamino or di(lower)alkylamino.
 2. The compound according to claim 1, wherein the aromatic ring-containing organic group is dansyl.
 3. The compound according to claim 1, wherein the aromatic ring-containing organic group is dansylamino(lower)alkyl.
 4. The compound according to claim 1, wherein the aminopolyacetic acid comprises a straight or branched chain or cyclic hydrocarbon, and contains a total of at least two amino groups which interrupt or are substituted at a terminal end of said hydrocarbon, the total of said amino groups being substituted with at least three acetic acid groups.
 5. The compound according to claim 1, wherein the aminopolyacetic acid is ethylenediamine tetraacetic acid, diethylenetriamine pentaacetic acid, trans-1,2-cyclohexadiamine tetraacetic acid or 1,4,7,10-tetraazacyclododecane tetraacetic acid.
 6. A complexing agent for a metallic element which comprises the chelating compound according to claim 1 wherein R in formula I is selected from the group consisting of naphthyl(lower)alkyl, naphthylamino(lower)alkyl, naphthalenesulfonylamino(lower)alkyl and dansylamino(lower)alkyl and having a chelating property and a specificity for a hepatobiliary organ or tissue. 